There are a large number of liquid degassing processes in the petroleum chemical industry, coal chemical industry, food, water treatment, oil and other industries. Efficient and economical degassing technology plays an important role in the efficient, safe and long-termoperation of the device. In the petrochemical industry, the release of dissolved gas from liquid due to pipe pressure drop in the pressurized liquid delivery process may cause air resistance, local corrosion and other issues. In the food industry, dissolved gases affect the purity of the products, and lead to the quality problems. The existence of dissolved oxygen in water treatment process is the main reason for the corrosion of the thermal equipment (such as steam turbine, etc.), resulting in the oxygen corrosion of the boiler during operation and out of operation. The dissolved gas in the fine chemical industry can cause bubbles defects in products. Therefore, liquid degassing technology is widely used in the process industry, and plays an important role.
At present, the main technology of liquid degassing is divided into two kinds: physical or chemical. The principle of the physical method is Henry's Law (the solubility of gas in water is directly proportional to the partial pressure of the gas at the surface of the solution) and that of Dalton's partial pressure law (The partial pressure of various components in a mixed gas is proportional to the its mole fraction). By changing the partial pressure and gas component content, the dissolved gas in the liquid is removed. Physical methods include air blast vacuum and membrane separation technology. In chemical methods, adsorption materials are added into the liquid, and dissolved gas is removed by reacting with the adsorbent material in the liquid under partial pressure. The blast type, and vacuum type technology has certain application limitations because of large area requirement, relatively high operating costs. The need to use blowers, vacuum pumps and degassing tower (tank) or combination thereof limits its use to substantially atmospheric or low pressure conditions. Membrane separation is carried out by the pressure difference between the inside and outside of a membrane. Gas can be passed through the membrane and the liquid cannot. Membrane separation technology is not suitable for the degassing process of high-pressure liquid containing solid impurities. In recent years, with the continuous progress of science and technology, a method has been developed by using ultrasonic wave and swirling technology to carry out the degassing. Ultrasound technology uses the hole effect of ultrasonic vibration. The diameter of and the rising rate of the micro-bubbles in the fluid increase, and finally rise to the surface, discharged from the exhaust port, eliminating tiny bubbles in the fluid. Swirling technology realizes the removal of trace gases in liquid by the use of liquid-gas two-phase density difference in a centrifugal field.
In comparison, the swirling degassing technology can be applied in solids-containing liquid degassing and high-pressure degassing processes. The researchers through extensore research have also invented a number of three-phase separators applied in the separation of sand and swirling degassing from crude oil in the field of oil production processes, and the use of a certain structure to enhance the effect of swirling degassing, such as the use of inverted cone structure to optimize the structure of the swirling degassing device, etc. (Zhang Yujie, Jiang Minghu, Zhao Lixin et al. Flow field analysis and structure optimization of three phase separator based on CID. Chemical engineering machinery, 2010; Liu Xiaomin, Jiang Minghu, Zhao Lixin et al. Development and feasibility test of gas—liquid swirling separation device. Fluid machinery, 2004; Wang Hanlun, Chang Zheng, Xu Lei et al. Study on pressure characteristics and separation characteristics of the integrated swirler with degassing and removal of sand, chemical equipment technology. 2010; Jiang Minghu, Han dragon, Zhao Lixin et al. Study on separation performance of inner cone type three phase swirling separator. Chemical machinery. 2011). Because swirling degassing is bared on by the principle of liquid-gas two-phase density difference, the change of the flow field in the swirling degasser has a great influence on the variation of centrifugal field, thereby affecting the degassing efficiency. For example, the fluctuation of inlet flow can cause the change in the size of the centrifugal field, and the change of operation conditions such as the change of inlet air volume can affect the thickness of the air column in the swirler. For a given overflow outlet size, the change of the diameter of the air column will directly result in a large amount of liquid carried in the outlet for gas or gas carried in the outlet for liquid, requiring a second separation after the separation by the separator. FIG. 2 is a schematic diagram of the structure of the conventional swirling degassing device. When the flow rate of inlet is low and the centrifugal field is also low, the gas column diameter is smaller than that of the overflow port, and the outlet for gas phase can carry a large amount of liquid. Similarly, the flow rate of inlet is constant, and the entrainment of inlet gas is reduced, which also has the problem. When the flow rate of the inlet increases or the inlet gas content increases, it will lead to the increase of gas column diameter, which results in the reduction of gas phase separation efficiency and other issues. On the other hand, researchers have discovered that conventional technology is suitable only for the working conditions of trace gas carried in the liquid, and does not perform well in conditions of a large amount of gas carried in the liquid.